Late 16th century Russian abacus The Russian abacus or schoty (literally "counts") is a decimal type of abacus that has a single slanted deck in a unique vertical layout, with ten beads on each wire (except one wire which has four beads, for quarter-ruble fractions, that is usually near the user). It was developed in Russia from the late 16th century, at the time when abacus already was falling out of use in the Western Europe. However, the decimality of the Russian abacus (explained by Russian ruble's being the world's first decimal currency) and its simplicity (compared to the previous European and Asian versions) led to the wide use of this device in Russia well until the advent of electronic calculators in the late 20th century, though it remains in quite common use today. 1550 Streltsy First known standard military uniform worn by Russian regular army, elite armed forces known as Streltsy. 1552 Battery-tower The battery-tower is a late type of siege tower, carrying artillery inside it, a development of the gulyay-gorod concept. The first such tower was built by the Russian military engineer Ivan Vyrodkov during the siege of Kazan in 1552 (a part of the Russo-Kazan Wars), and could hold ten large-calibre cannons and 50 lighter cannons. Later battery-towers were often used by the Ukrainian Cossacks. 1561 Saint Basil's Cathedral Saint Basil's Cathedral is perhaps the most famous Russian Orthodox cathedral, a symbol of Moscow and Russia. It was designed by Postnik Yakovlev on the order of Ivan IV of Russia and built on the Moscow's Red Square in 1555–1561, to commemorate the capture of Kazan and Astrakhan. The unique feature of the Saint Basil's Cathedral is the fact that it is a complex of multiple temples put together. The original building, known as "Trinity Cathedral", contained eight side churches covered with onion domes and arranged around the ninth, central tented roof church of Intercession; the tenth church was erected in 1588 over the grave of venerated local Fool Vasily (Basil). In the 16th and the 17th centuries the cathedral, perceived as the earthly symbol of the Heavenly City, was popularly known as "Jerusalem" and served as an allegory of the Jerusalem Temple in the annual Palm Sunday parade attended by the Patriarch of Moscow and the Tsar. Its striking design, shaped as a flame of a bonfire rising into the sky, has no analogues elsewhere in the